1. Field of the Invention
The present invention relates generally to voting solenoid-operated valve devices for testing and controlling industrial process systems, and more particularly to a variable function voting solenoid-operated valve apparatus that provides low-cost, high-reliability testing and control of a fluid media processing or manufacturing plant.
2. Background of the Invention
Modern process or manufacturing plants consist of innumerable individual components. These components are integrated to form operational systems controlled by instrumentation and control systems consisting of a variety of sensors and controllers. The operational and control systems serve not only to achieve desired process conditions and parameters, but also to allow a plant facility to safely modify or discontinue operation of all or a portion of the plant's systems and components in order to avoid predetermined deleterious activities and conditions.
For example, safety systems or configurations require routine testing and maintenance in order to verify their continued proper performance with respect to the plant functions for which they were intended. From both an operational and economic vantage, it is highly desirable that such safety systems or configurations should not unnecessarily modify or discontinue operation of the plant systems or components being monitored. One manner in which such safety systems or configurations function is by the isolation or venting of certain process fluids when an unsafe operating condition has been detected by the safety system or configuration. Depending on a particular processing or manufacturing plant's intended operational parameters, this isolation and/or venting of process fluids can be accomplished by actuating process valves. When these process valves are pneumatically actuated spring return type valves, either applying pressure or venting pressure to the valve actuator will move the valve to the open or closed position. One of the means by which pneumatic supply is controlled to the process valves is through the use of one or more solenoid-operated valves.
In function, the solenoid-operated valves of such safety systems or configurations serve to initiate a process whereby a fluid or pneumatic supply is either applied to or vented from the process valve actuator when one or more operatively associated solenoid-operated valves changes state or position in a predetermined manner, e.g., when the solenoid-operated valve is de-energized by the logic control system. The plant processing system and any subservient system or component controlled thereby is then placed in an operational configuration pre-designated as a “safety action”.
It is frequently the case that testing and maintenance of an individual solenoid valve should be accomplished without initiating the safety action, thereby avoiding an undesired modification or discontinuance of the plant process system being monitored. However, most prior solenoid valve configurations have necessarily required a trade-off by operators between either discontinuing safety monitoring during testing and maintenance or risking false initiations of the safety action as a result of limited or incomplete testing and maintenance.
For example, a “1 out of 1” solenoid-operated valve configuration is well-known in the art wherein a single solenoid-operated valve is employed for activating the system's safety action by actuating process valves upon detection of an unsafe condition. Such configurations can achieve high plant safety availability when solenoid-operated valve operation is regularly tested by de-energizing the solenoid-operated valve and then monitoring a venting of the fluid or pneumatic supply through an exhaust body such as an anodized aluminum or composite material manifold or the like. Since the process valve and ultimately the plant process system (or its constituent components) may be affected by such venting, testing of the solenoid-operated valve can only be performed under plant bypass conditions, wherein the fluid or pneumatic supply is allowed to pass directly to the process valve or its constituent components by means of a bypass valve. When the solenoid-operated valve is bypassed for testing, the safety action (actuation of the process valve) intended to avoid the unsafe condition cannot be initiated by the solenoid-operated valve.
In practice, the overall safety availability performance of a 1 out of 1 solenoid-operated valve is therefore limited by the percentage of operational time required in a bypass state for testing and maintenance. Moreover, such configurations can achieve only relatively low plant system reliability outside of testing and routine maintenance, since an unexpected component failure within the solenoid-operated valve, for example, a coil failure, will necessarily cause an inadvertent venting or isolation of the fluid or pneumatic supply, i.e., actuation of the process valve and initiation of the safety action.
A “1 out of 2” solenoid-operated valve configuration is also known wherein correct functioning of only one of a pair of solenoid-operated valves connected in operative association is required to actuate the process valve and initiate the safety action. Since only one of the solenoid-operated valves is required to actuate the process valve, relatively high plant safety availability is inherently provided.
Moreover, such a configuration does not require the high testing frequency of the 1 out of 1 solenoid-operated valve system; however, routine testing and maintenance of the device are still required for ordinary safety applications. Similar to the 1 out of 1 solenoid valve, the 1 out of 2 configuration typically requires bypassing the system's safety action during testing. Accordingly, the device is incapable of actuating te process valve, and of isolating or venting the process fluid supply in response to an unsafe condition while the system is in bypass mode. Thus, the safety availability performance of the 1 out of 2 solenoid is also limited by the percentage of operational time required for bypassing and testing. Moreover, since there are two discrete solenoids capable of initiating the safety action, a failure in a single solenoid-operated valve coil can lead to the inadvertent actuation of the process valve and isolation or venting of the process fluid.
A “2 out of 2” configuration has also been employed wherein both solenoid-operated valves must correctly function to actuate the process valve and initiate the safety action. Since both solenoid-operated valves must function properly, high plant system reliability is readily obtained. However, since the likelihood of individual component failure within the solenoid-operated valve system is effectively doubled (for example, both solenoid-operated valves must always function properly), the configuration suffers from relatively low safety availability unless function-tested very frequently. Also, initiation of the safety action is again prevented during testing and maintenance because the plant system must be bypassed for such functions, wherein the fluid or pneumatic supply is allowed to pass directly to the process valve or its constituent components by means of a bypass valve. When the solenoid-operated valves are bypassed for testing, the safety action, actuation of the process valve, intended to avoid the unsafe condition cannot be initiated by the solenoid-operated valves. The testing and maintenance cycle is generally time and manpower intensive since most of the known 2 out of 2 configurations are still tested manually. As with the previously discussed solenoid-operated valve systems, therefore, the safety availability performance of the device is limited by the percentage of operational time required during bypassing and testing or maintenance.
A more sophisticated approach has involved a “2 out of 3” voting solenoid-operated valve system wherein two out of three solenoid-operated valves must operate properly to actuate the process valve and isolate or vent the process fluid. The configuration achieves high safety availability since only two of the three solenoid-operated valves must function to initiate a safety action, and high plant system reliability since two of the three solenoid-operated valves must experience a coil failure or the like for an inadvertent actuation of the process valve and isolation or venting of the process fluid supply to occur. The safety availability is also superior to the previously discussed solenoid systems insofar as the device can be tested or maintained without bypassing the safety action.
In practice, however, those of skill in the pertinent arts have found that the use of three solenoid-operated valves substantially increases the overall price of the system. Moreover, additional logic control system input and output points are required relative to simpler configurations, and thus installation and operating expenses are also increased. In short, the high costs associated with the 2 out of 3 solenoid configuration have virtually negated its effective industrial utility.
Finally, elaborate “quad-voting” configurations have also been attempted wherein both high safety availability and high plant system reliability are reportedly achieved. However, the use of four solenoid-operated valves in a voting configuration has been found to require an unusually large amount of space to accommodate its complex pneumatic tubing, and such complexity obviously increases the associated capital and installation costs. Perhaps even more importantly, many commercial operators of voting solenoid-operated valve systems have been found to particularly disfavor the complex quad-voting configuration because of the elevated potential for testing and maintenance error associated therewith.